1. Field of the Invention
The invention relates to an electronic component capable of being welded to a circuit board. More particularly, the invention relates to a surface mounted electronic component.
2. Description of Related Art
To reduce sizes of electronic products, a surface mount technology (SMT) is widely applied to the present electronic products (such as computer products, home appliances, electronic toys, electronic equipments). Especially, functions of mobile electronic products such as mobile phones, personal digital assistants (PDAs), notebooks, etc., become versatile, and sizes and weights thereof become smaller and lighter. The SMT is a latest assembling and welding technique in a machining process of combining electronic components and a printed circuit board (PCB).
The assembling and welding method of the SMT is to use a solder paste screen printer to print solder paste on a pad surface of the PCB, and then uses a mounter to mount surface mount devices (SMDs) to the pads. The SMDs include resistors, capacitors, inductors, diodes, transistors and/or integrated circuits (ICs), etc. A hot air reflow process is performed to the PCB mounted with the solder paste and the SMDs to melt the solder paste, so as to combine the SMDs and the pads of the PCB, and now the assembling and the welding are completed.
To cope with requirement of lightness, slimness, shortness and smallness of the electronic products, an assembling density of the devices on the PCB is increased. To avoid a problem of mount offset, etc., an assembling precision of the SMDs is highly required. To cope with a requirement of the assembling precision, a size of a conductive electrode of a general SMD is required to comply with a size of the pad on the PCB. FIG. 1A and FIG. 1B are diagrams illustrating pads of different sizes matched to the corresponding sizes of conductive electrodes. Referring to FIG. 1A, if pads 111 on a PCB 110 of a certain client are designed to have a large size, an SMD 120 must have relatively large conductive electrodes 121. Referring to FIG. 1B, if pads 131 on a PCB 130 of another certain client are designed to have a small size, an SMD 140 must have relatively small conductive electrodes 141 even if the SMD 120 and the SMD 140 have a same device size (for example, 3 mm×3 mm) or a same characteristic specification (for example, the SMDs are all resistors of 1 mΩ). Namely, regarding the SMDs having the same device size or characteristic specification, the SMDs having different sizes of the conductive electrode have to be designed and manufactured according to different pad sizes required by different clients.
Conventionally, if the SMD with a single type of package is welded to the pads of different sizes, the SMD is probably slid in case that the solder paste is melted, which may cause problems of inaccurate alignment and unstable welding, etc., so that the assembling precision cannot be satisfied. For example, if the SMD 140 of FIG. 1B is welded on the pads 111 of FIG. 1A, in case that the solder paste is melted, the relatively small conductive electrode 141 is probably slid within a range of the large pad 111. If the SMD 120 with relatively large conductive electrodes 121 of FIG. 1A is welded to the relatively small pads 131 of FIG. 1B, a similar problem is also encountered.
Therefore, regarding the conventional technique, a manufacturer requires to design and manufacture a plurality of types of SMDs with different conductive electrode specifications, so as to match the pads of different sizes. Since the SMDs of the same characteristic specification must have different conductive electrode specifications, a production control thereof is complicated. Moreover, to satisfy client's design requirements of different pad sizes, the SMDs of different conductive electrode specifications have to be stocked, which may increase an inventory cost.